Figure 1.

Mitochondria exert transcriptional control over gene programs involved in oxidative metabolism and thermogenesis. Transcriptional control is dependent on mitochondrial respiratory capacity. In this model, impaired respiratory capacity acts as a transcriptional checkpoint, whereas augmented respiratory capacity acts as a transcriptional trigger. In humans and mice, obesity is associated with reduced brown fat function. Our model may explain the inverse association between respiratory capacity and thermogenic gene expression in brown fat of certain obese mice (eg. ob/ob) and perhaps obese humans.